1. Field of the Invention
The disclosure discloses a communication system and a method for cancelling timing dependence within signals of the communication system.
2. Description of the Prior Art
In a conventional fast Ethernet, since a transmission signal Tx and a receiver signal Rx are transmitted with a pair of transmission lines for a same receiver, the transmission signal Tx and the receiver signal Rx will not interfere with each other. Under the spec of the high definition multimedia interface 1.4, the spec of the above-mentioned fast Ethernet is also utilized so that the interference between the signal will not occur, however, under the limitations of transmission media, the transmission signal Tx and the receiver signal Rx have to be transmitted on a same transmission line.
Since the high definition multimedia interface transmits the transmission signal Tx and the receiver signal Rx with a single transmission line, either the transmitter or the receiver receives signals from each other and certain reflected echoes. When the reflected echoes are getting significant, the signal-to-noise ratio of the communication system is getting higher as well so that the echoes are required to be reduced by additionally using an echo canceller.
A conventional echo canceller updates a set of coefficients by using least mean square (LMS), since a corresponding frequency response is getting convergent with the aid of using least mean square to incur a finite frequency response, which reduces amplitudes of the echoes within the signals. A primary condition of using the echo canceller lies on timing independence between received transmission signals Tx, so that different transmission signals received in consecutive moments will not interfere with each other.
However, when the fast Ethernet utilized the multi-level transmit-3 (MLT-3) protocol in encoding, the timing independence between transmission signals cannot be fulfilled so that the echo canceller cannot be utilized. Signals encoded by the MLT-3 protocol acquire values of −1, 0, and +1. Besides, when there are two consecutive MLT-3 encoded signals acquiring a same value 0, it indicates that two corresponding transmission signals Tx acquire a same value as well. Since probabilities of the MLT-3 encoded signals being 0 and 1 are 50% respectively and independently, the probability that two consecutive transmission signals acquire a same value will be 50% as well so that timing dependence occurs between both the transmission signals. Therefore, while retrieving least mean square by using the echo canceller, the frequency response of echoes cannot be convergent so that amplitudes of the echoes cannot be effectively reduced.